1. Field of the Invention
This invention relates to a hydrostatic drive system with a pump and at least one consuming device that is connected to the pump and can be actuated by a control valve. In particular, the control valve can be actuated as a function of an actuator that specifies a desired speed of movement and a direction of movement of the consumer, and the control valve, in the neutral position, makes possible an unpressurized circulation of the pump.
2. Background Information
Similar hydrostatic drive systems in which a pump, for example a pump with a constant delivery volume, is provided for the pressurization of a plurality of consuming devices, and when the consuming devices are not actuated, the pump is operated in an unpressurized circulation, are used in machines, for example in fork-lift trucks, to actuate the hydraulic work system.
The prior art discloses systems in which the control valves are directional control valves that throttle the flow in intermediate positions and have an open neutral position. Therefore, the control valves are also designated open-center control valves that can be actuated by a human operator as a function of the deflection of the actuator. When the directional control valve is deflected, the directional control valve throttles the unrestricted circulation of the pump and connects the delivery line of the pump with the hydraulic line that leads to the consuming device. A pressure is thereby built up in the delivery line, as a result of which the consuming device is set in motion. A desired speed of movement of the consuming device is specified by the opening width of the directional control valve as a function of the deflection of the actuator. The delivery current of the pump not required by the actuated consuming device flows via the unrestricted circulation of the directional control valves to the reservoir. When a plurality of consuming devices that have different load pressures are actuated simultaneously, however, operating conditions can occur in which an excessive hydraulic flow is delivered to the consuming device that has the lower load pressure. To prevent an increase in the speed of movement of the consuming device that has the lower load pressure, the corresponding directional control valve must be modulated into a switched position that throttles the admission to the consuming device. As a result, however, there is an increased amount of effort required on the part of the operator who is operating the drive system, because when the operator has to actuate a plurality of consuming devices simultaneously, he must readjust the speed of movement of the consuming devices by a corresponding deflection of the actuator.
The object of this invention is to make available a hydrostatic drive system of the type described above that easily and economically makes it possible to operate the consuming devices independently of the load.